It is well known that plastic is cheaper than silicon so the question is why not collect a large amount of sunlight and focus it via a cheap flat plastic Fresnel lens onto silicon PVs (photovoltaics)? Well we do such, called CPV (concentrated PV) but the problem is we're also concentrating the out-of-band infrared, (IR), and ultraviolet, (UV), spectral components which do not create electricity. Instead these create heat which warms up the PV and its conversion efficiency plummets. Thus, CPV systems utilize heat sinks, often running water through the heat sinks, to cool the system but that is expensive and cumbersome.
CPV systems also typically use multi-junction PVs and materials other than silicon in order to extend their responsivity further into the IR and the UV but these are expensive and there is always some out-of-band energy remaining which heats up the system and limits its efficiency. We prefer to remove the heat sources from the sunlight before it even hits the PV and hence utilize some type of optical filtering. This is also done but the optical filters are placed on top of the PV and so they still conduct a lot of heat into the PV.
We have found (see U.S. Pat. No. 8,710,353 to Shepard, which is incorporated by reference in its' entirety) that via the use of optical waveguides (e.g., bundles of optical fiber) as filtering elements; we can absorb the out-of-band spectral components, thereby converting them into heat which is either conducted into solar-thermal energy converters or radiated into the air so that the heat is not conducted to the PV. This permits higher levels of concentration (thereby pushing the “plastic is cheaper than silicon” advantage) while also eliminating the need for heat sinking systems on the PV.
Currently losses in the visible range of the spectrum are too high to permit “solar over fiber” except for short distances. Herein we solve that problem, thereby enabling secure optical power distribution networks (which have many advantages over their electrically cabled counterparts) and extend the capabilities of waveguide filters for PV and solar-thermal systems.
Enabling low-loss transmission of visible frequencies over optical waveguides also greatly expands on the capabilities of prior art in the area of balloon-type solar collectors. Currently these place PVs at the focal point of an inflatable balloon which has a reflective surface to form a mirrored collector. See Colfax, Tyler, Solar Balloons: Future of Alternative Energy, 23 Sep. 2008.
Our new balloon-type solar collectors however place our new optical waveguides at the focal point. These can be lightweight and so can extend high into the sky or even float. Note that such large-scale balloon type collectors are only feasible when used in conjunction with our new optical cabling methods. The weight alone of PVs placed inside such a large-scale buoyant balloon would be prohibitive; and at such high optical intensities these would require extensive cooling systems and thick electrical cabling which further prohibit the prior art from “harvesting the sky” in such a way.
We also expand on the capabilities of prior art via mode-coupling the solar energy into the PVs—rather than just shining the light onto a PV in which case a large amount reflects. In our embodiments the PVs can receive all of the light imported to them via our waveguides.
Moreover, our optical power cabling cannot “short circuit” in water while it safely distributes power to PVs on land or inside buildings. Thus, we enable the floatation of balloon/bulb type collectors on a body of water, whereas electrical cabling from PVs placed over water is a daunting proposition. Just as our solar balloons minimize the terrestrial footprint by expanding the collector into the sky, they can also take advantage of the fact that area on water is often less expensive real-estate than the same area on land. The direction insensitivity of some of our novel collectors simplifies their application to turbulent water; and installation costs (on land or water, or from a window, car or backpack) can be reduced to those of simply “blowing up a balloon.”
Thus, the need exists for solutions to the above problems with the prior art.